The need for developing large clamping forces in connectors for securing two members together has long been recognized. Providing large clamping forces is especially important when the connector is to be used for connecting two tubular members of an underwater well installation, since the connection must then be such as to withstand not only large forces resulting from component weight and the actions of waves and currents but also large internal fluid pressures. In the underwater well field, connectors of this general type have reached an advanced state of development as disclosed, for example, in U.S. Pat. Nos. 2,962,096 Knox, 3,228,715 Neilon et al 3,321,217 Ahlstone, 3,333,870 Watkins, 4,200,312 Watkins, 4,209,193 Ahlstone.
All of the successful prior art connectors employed in the underwater well field for developing high clamping forces appear to employ annular locking means, varying from annularly arranged collets or annularly arranged arcuate segments to a single split locking ring, the locking means being carried by one of the members to be connected, the other member presenting an annular groove with which the locking means engages. Opposed transverse end faces are provided, each on a different one of the members being connected or on a different one of the connector members, the transverse end faces being disposed to be clamped together as the connector is made up, the annular locking means and groove having mating frustoconical shoulders so arranged as to generate the large clamping force to clamp the end faces together as the locking means is forced into engagement in the groove. When the connector is to be made up in an underwater location not directly accessible for manual operations, the connector is provided with a power device or devices, usually one or more fluid pressure operated rectilinear motors, for actuating the locking means. To convert the action of the power device into effective movement of the locking means, it has become a standard practice to have the power device force a camming ring axially relative to the members to be connected, the camming ring having a frustoconical camming face which slidably engages the locking means to force the locking means generally radially into engagement with the groove.
Though such connectors have achieved considerable success and wide acceptance in the field, requirements imposed by the users and potential users of such connectors have become increasingly difficult to satisfy. This difficulty is particularly severe in the underwater well field, where the water depths in which wells are being drilled have greatly increased, with an attendant increase in the forces, both external and internal, which must be accommodated by the connector. As an example, it is to be noted that some underwater wellheads are now being specified to withstand internal pressures as great as 15,000 p.s.i., so that that magnitude of pressure must be accepted by, e.g., the connector which secures the blowout preventer stack to a wellhead lower body. Thus, while there has in all events been a continuing need for improving such connectors, that need has been amplified by the increasing severity of potential users' specifications.
A particular problem posed by the need for very large clamping forces in such connectors arises because, on the one hand, the power available from acceptable power devices is limited by size constraints for the power device or devices while, on the other hand, losses due to friction at the camming surfaces demand large actuating power if actuation of the locking means is to result in the desired large clamping forces. Though workers in this field have expended much effort in attempting to overcome that and other problems, overall effectiveness of such connectors has failed to keep pace with the increasing need for improvement.